Polyolefins and other polymers are frequently modified in order to improve their rheological and other physical properties. Various chemical agents have been used to carry out such modifications.
One method for modifying polymers, such as polyolefins, is to use molecules that are capable of providing a nitrene reactive group(s) for insertion into C—H bonds on the polymers. An example of such a class of chemicals are the sulfonyl azides which are disclosed in WO 99/10424 published Mar. 4, 1999, which is hereby incorporated by reference for its teachings regarding azides. When heated to an appropriate reaction temperature, these azides decompose to form nitrene groups that can then insert into C—H bonds on the polymers. These sulfonyl azides are effective for providing nitrene groups for insertion into the C—H bonds of styrenic based and polyolefin based polymers.
However, sulfonyl azides and other azides can be shock sensitive. It may be necessary to phlagmatize the azides or to otherwise protect the azides from reaction during the manufacture and processing of the azide and the shipping and handling of the azide. However, the methods that would typically be used to protect chemicals such as azides from reacting can be expensive and may not be compatible with the polymers that are to be modified. Additionally, polymers are often used for packaging food. Therefore, it is important that the addition of the protective agent not prevent the modified polymer from being approved for food packaging applications.
What is desired is a relatively inexpensive and easy manner for phlagmatizing a coupling agent that also does not interfere with the coupling agent or limit the use of the coupling agent for producing modified polymers.
As used herein, the following terms shall have the following meanings:                (a) “Coupling Agent” shall mean a chemical compound that contains at least two reactive groups that are each capable of forming a carbene or nitrene group that are capable of inserting into the carbon hydrogen bonds of CH, CH2, or CH3 groups, both aliphatic and/or aromatic, of a polymer chain. The reactive groups together can couple or cross-link polymer chains. It may be necessary to activate a coupling agent with heat, sonic energy, radiation or other chemical activating energy, for the coupling agent to be effective for coupling and/or cross-linking polymers chains.        (b) “Phlagmatizing” refers to methods for reducing the shock sensitivity of a chemical or chemical species by mixing or combining the reactive chemical with an inert or less reactive chemical.        (c) “molecular melt” refers to an at least partially amorphous blend, at room temperature, of a coupling agent (modifying agent) and an antioxidant, optionally also containing other polymer additives. Both the coupling agent (modifying agent) and the antioxidant are at least partially contained in the amorphous phase of the blend. Also, preferably the coupling agent (modifying agent) and the antioxidant form a complex where the Raman spectra relating to the groups forming the nitrene groups are shifted compared to the Raman spectra exhibited by the groups forming the nitrene groups of the coupling agent alone.        (d) “antioxidant” refers to types or classes of chemical compounds that are capable of being used to minimize the oxidation that can occur during the processing of polymers. The term also includes chemical derivatives of the antioxidants, including hydrocarbyls. The term further includes chemical compounds, as described later in the description of the antioxidant, that when properly combined with the coupling agent (modifying agent) interact with to form a complex which exhibits a modified Raman spectra compared to the coupling agent or modifying agent alone.        (e) “modifying agent” refers to a chemical compound that contains a reactive group capable of forming a carbene or a nitrene group that can react with a polymer chain.        (f) “target polymer” refers to a polymer that is intended to be modified by the coupling or modifying agent. The target polymer can be any polymer that contains CH, CH2, or CH3 groups, aliphatic or aromatic, of a polymer chain. Preferably, the target polymer can be any polyolefin (including polyethylene) or styrenic based polymer.        (g) “DSC” refers to a differential scanning calorimeter or differential scanning calorimetry analysis, depending on the context it is used in. DSC is a method one of ordinary skill in the art is familiar with to determine the crystallinity of a polymer.        (h) “Nitrene group” refers to a compound having a structure R—N, where N is nitrogen capable of reacting with a polymer chain by inserting into the carbon hydrogen bonds of CH, CH2, or CH3 groups, both aliphatic and/or aromatic, of a polymer chain. It is believed that the nitrogen most preferred for inserting into the carbon hydrogen bonds has two lone pairs of electrons. R may be any atom or atoms that do not adversely interfere with the nitrogen inserting into the above-described carbon hydrogen bonds.        (i) “Carbene group” refers to a compound having a structureR—C—R′        where C is carbon capable of reacting with a polymer chain by inserting into the carbon hydrogen bonds of CH, CH2 or CH3 groups, both aliphatic and/or aromatic, of a polymer chain. It is believed that the carbon most preferred for inserting into the carbon hydrogen bonds has one lone pair of electrons. R and R′ are independently any atom or atoms that do not adversely interfere with the carbon inserting into the above-described carbon hydrogen bonds.        (j) “DPO—BSA” refers to the following compound:        4,4′-Oxydibenzenesulfonyl azide.        